1. Field of the Invention
The present invention relates to an apparatus which inspects patterns formed on objects, particularly to a pattern defect inspection apparatus which inspects defects in patterns formed on objects such as photo masks employed in semiconductor manufacture and a pattern defect inspection method.
2. Description of the Related Art
As one of the causes of degradation of yield in the manufacture of large scale integration (LSI) is raised pattern defects occurring on the photo mask employed in producing a semiconductor device by the photolithography technique. Various types of pattern defect inspection apparatuses inspecting such defects have been developed and used already.
The patterns of photo masks to be inspected by the pattern defect inspection apparatus are formed by patterning a metal film of chrome (Cr) deposited on a glass substrate by means of exposure and etching processes. The quantity of undercut of the pattern, anisotropy, and pattern conversion difference changes according to patterning by wet etching, patterning by dry etching or the etching condition.
The sidewall of the actual mask pattern may not be a complete perpendicular sidewall. The optical measurement image of the pattern may not be a complete monochrome color code pattern. The boundary between the patterns may be blurred and the edge of the pattern may be unknown. In this case, the dimensions of the pattern, line width thereof or the position of a pattern edge varies to some extent from the pattern data of the design data that is the criteria of inspection. As a result, the pattern is recognized as a defect by the pattern defect inspection apparatus. For the purpose of solving this problem, the conventional pattern defect inspection apparatus develops pattern design data in pattern data, subjects the pattern data to a resizing process, and matches the pattern data with the pattern of the photo mask. In this resizing process method, design data used in drawing a pattern is developed to a grayscale pattern data. Then, the grayscale pattern data is classified into vertical and horizontal grayscale pattern data and diagonal grayscale pattern data on the basis of output results of a device for detecting a maximum level of grayscale pattern data and a device for detecting inclination of the pattern. The classified pattern data are revised individually.
As a result, the dimension or line width of the pattern data of the design data is matched with the pattern on the photo mask. The observed value obtained by detecting the transmitted light corresponding to the pattern formed on the photo mask by means of a sensor and the pattern data revised as described above are compared by defect detecting means to detect a defect.
However, this kind of pattern defect inspection apparatus includes the following problem. In other words, the grayscale pattern data is classified into vertical and horizontal grayscale pattern data and diagonal grayscale pattern data when the grayscale pattern data obtained from the design data and pattern of the photo mask are matched with each other. However, a proper resizing process cannot be performed in a small change part (corner part) of the pattern data of OPC (Optical Proximity Correction) patterns and so on, which have become more and more complicated recently. For this reason, the small change part of pattern data may be detected as a nuisance defect of pattern data.
As described above, the conventional pattern defect inspection apparatus compares the grayscale pattern data obtained by developing, by means of a pattern developing device, the design data used when drawing a pattern on the photo mask, with the measurement data generated by optically scanning a pattern drawn on the photo mask. For this reason, the conventional pattern defect inspection apparatus has problems such that it is impossible to perform matching of pattern data in correspondence with the subtle change of a pattern occurring by the etching process and complicated pattern shape, in the resizing process.